It is well known to form coatings on metal surfaces to serve as a base for lubricants and/or to give corrosion resistance or paint adhesion by treating the metal with a phosphate solution. It is equally well known that a problem of such processes is that a tightly adherent scale of metal phosphates tends to build up in the apparatus being used. If scale does form, the process is still operable but is less economical. Numerous attempts to prevent this adherent scale have been made, often involving the addition of various additives, such as polyacrylamides and carbohydrates, to the treatment solution. Only some of these attempts have been successful. British Pat. Specification Nos. 1,257,947, 1,408,702, and 1,412,135 are amongst the many disclosures of such attempts.
When the metal surface needs to have a lubricant composition applied to it to facilitate cold working operations such as drawing it is customary to apply the lubricant after applying the phosphate coating but it has been proposed to form the phosphate coating and apply the lubricant in a single step. Such a process, and compositions for it, are described in British Pat. Specification No. 1,421,386. Such compositions already include relatively large amounts of cationic surfactant. Despite the presence of these surfactants and that, as described therein, the solution scavenges the sludge forming materials that normally form in phosphating solutions a fundamental difficulty with processes of the type described in Specification No. 1,421,386 is that a tightly adherent wax scale forms on the apparatus being used. It seems probable that some form of reaction occurs between the metal of the apparatus and the fatty component of the lubricant but whatever the mechanism the result is that a scale is formed. This scale chemically is very different from the phosphate scale described above in that it includes large amounts of tightly adherent fatty material. Although it might be expected that emulsifiers and surfactants would inhibit the scale, it is formed despite the presence of large amounts of emulsifier and the addition of further emulsifier or common surfactants does not prevent its formation. Despite the theoretical advantages of the process of Specification No. 1,421,386 and despite attempts at avoiding the scale problem, scale formation has proved to be such a problem that the process is commercially impracticable.